31 lines
1.0 KiB
Plaintext
31 lines
1.0 KiB
Plaintext
/**
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Join an array of strings and/or numbers using the given string as a delimiter.
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Use-case: Defining key paths in a nested object. For example, for dot-notation fields in MongoDB queries.
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@example
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```
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import type {Join} from 'type-fest';
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// Mixed (strings & numbers) items; result is: 'foo.0.baz'
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const path: Join<['foo', 0, 'baz'], '.'> = ['foo', 0, 'baz'].join('.');
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// Only string items; result is: 'foo.bar.baz'
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const path: Join<['foo', 'bar', 'baz'], '.'> = ['foo', 'bar', 'baz'].join('.');
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// Only number items; result is: '1.2.3'
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const path: Join<[1, 2, 3], '.'> = [1, 2, 3].join('.');
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```
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@category Array
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@category Template literal
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*/
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export type Join<
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Strings extends Array<string | number>,
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Delimiter extends string,
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> = Strings extends [] ? '' :
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Strings extends [string | number] ? `${Strings[0]}` :
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// @ts-expect-error `Rest` is inferred as `unknown` here: https://github.com/microsoft/TypeScript/issues/45281
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Strings extends [string | number, ...infer Rest] ? `${Strings[0]}${Delimiter}${Join<Rest, Delimiter>}` :
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string;
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